1. Field of the Invention
The invention relates to a shock absorber, in which compression and return damping is realized with double pistons and in which pressurization of the absorber is realized between the pistons.
2. Description of the Related Art
The Applicant produces a shock absorber 1, see FIGS. 1 and 1a, comprising a damping-medium-filled cylinder body 2, which is delimited at the ends and is divided into a first damping chamber C1 and a second damping chamber C2 by a main piston device that is made up of two main pistons 4, 5.
The main pistons 4, 5 are mounted on a hollow piston rod 3, which extends through one of the ends 2a of the cylinder body. Through the piston rod 3, damping medium flows between a pressurized chamber 6a into a pressurization reservoir 6 and a respective damping chamber C1, C2. The pressurized damping medium is led from the pressurization tank 6 via a duct 7 in the piston rod 3 to an interspace 8 between the main pistons 4, 5. The damping medium is led onward via continuous pressurization ducts 9, 10 extending through the main pistons 4, 5 and delimited by first flow limiters 11, 12, in order finally to be led out into the respective damping chamber C1, C2. One of the main pistons 4 damps motion substantially in a first direction R1, i.e. the compression direction, where the main piston device moves such that the shock absorber length decreases, and the other of the main pistons 5 damps motion in substantially another direction R2, i.e. the return direction, where the main piston device moves such that the shock absorber length increases. The damping is realized through deformation of a second flow limiter created by a collection of flexible first washers 15, 16, which delimit the main flow ducts 13, 14 extending through the main piston.
By virtue of this design, it is possible to ensure that a pressure markedly greater than zero always prevails in the damping chambers. This since the pressure in the damping chambers C1 and C2 is only marginally lower than the pressure P1, owing to the low fall in pressure over the flow limiters 11 and 12 and the fact that the interspace 8 common to both chambers is also pressurized at the same pressure. The pressurized damping medium is led out into the respective damping chamber C1, C2 via a collection of flexible second washers 11PA, 12PA, i.e. shims. The flexible second washers are fixed in place by their inner diameter such that they flex around their central part and let through a damping medium flow only via their outer part, which diverges from the first side of the main piston and therefore leaves an opening area which is disposed on the outer diameter of the second washers, see FIG. 1b. In order to achieve minimal flow resistance in the direction out from the interspace, the collections of flexible washers have been chosen to be as soft as possible such that they can open with just a very small pressure difference between the respective damping chamber and the interspace.
Problems have then arisen, since very soft washers easily become unstable and start to deform unpredictably with the flow. The whole of the dynamics of the absorber are in this case impaired and unexpected vibrations and noise can arise.
A further problem with shock absorbers produced according to the previously known method arises when the main pistons are mounted on the piston rod. In order not to create unwanted restrictions in the flow between the pressurization tank and the intermediate chamber, the pressurized damping medium flowing from the pressurization tank through the piston rod must have a large area to pass through. The previous solution has a separate intermediate part 17PA, which separates the two pistons. This intermediate part is difficult to fit, so that the flow paths 17PAa through the piston rod and the intermediate part end up centered one above the other and just a minor displacement between these parts creates a reduced flow area.
In order to alleviate the problem with centering of the flow paths, an internal recess 17PAb has been introduced in the intermediate part. In order to minimize the flow resistance, this recess has a large radial extent. The mounting of the main pistons on this intermediate part may also be a problem, since the intermediate part 17PA with its recess 17PAb is easily deformed when the main pistons are fitted by tightening of a retaining nut 20PA. In order to make it easy to change the damping character of the shock absorber by varying the washers (shims) with regard to size, thickness, number and mutual arrangement, then a simple and straightforward procedure must exist for the removal and fitting of the main pistons.